A multiple quantum well structure including a plurality of well-barrier pairs arranged along a direction is provided. Each of the well-barrier pairs includes a barrier layer and a well layer adjacent to the barrier layer. The barrier layers and the well layers of the well-barrier pairs are disposed alternately. A ratio of a thickness of the well layer in the direction to a thickness of the barrier layer in the direction in each well-barrier pair is a well-barrier thickness ratio, and the well-barrier thickness ratios of a part of the well-barrier pairs gradually increase along the direction.